Thermodynamics of the reduction of NADP with 2-propanol catalyzed by an NADP-dependent alcohol dehydrogenase

Abstract

The apparent equilibrium constant of the biochemical reaction, 2-propanol + NADP ox=acetone + NADP red, was determined at I=0.25 M over a wide range of pH (5.63 to 8.02) and temperature (5 to 40 °C). The reaction was catalyzed by an NADP-dependent alcohol dehydrogenase. The results were used to calculate thermodynamic quantities for the chemical (ionic) reference reaction: 2-propanol + NADP ox 3−=acetone + NADP red 4−+H +. The thermodynamic quantities for this reference reaction are as follows: equilibrium constant K=(5.98±0.46)×10 −10; standard molar Gibbs energy change Δ r G 0=(52.65±0.19) kJ mol −1 ; standard molar enthalpy change Δ r H 0=(38.9±0.6) kJ mol −1 ; and standard molar entropy change Δ r S 0=−(46.1±2.2) J K −1 mol −1 . All of these results pertain to 25 °C (298.15 K) and I=0. The results also lead, in conjunction with tabulated thermodynamic quantities, to the standard electromotive force E 0=−0.140 V for the reduction of NADP ox 3− to NADP red 4−.